Equation of normal to a curve

Slope: $$m_{\mathrm{normal}} = -\frac{1}{m_{\mathrm{tangent}}} = -\frac{1}{\left. \frac{dy}{dx} \right|_{(x_0,y_0)}}$$
Equation: $$y - y_0 = m_{\mathrm{normal}} (x - x_0)$$
Equation of the normal line (perpendicular to tangent) at point $$(x_0, y_0)$$.